In communication networks, information in the form of data is typically passed between endpoints. In order to achieve this, the data is often routed using one or more switches. Conventional switches may be used to establish circuits across the network or to route data units, typically formed as packets. Known circuit switches include space division switches, time multiplexed switches, S-T-S (space-time-space) switches; and T-S-T (time-space-time) switches. Known packet switches include asynchronous transfer mode (ATM) switches; internet protocol (IP) routers; and the like.
Both circuits and packets may be switched using a switch having buffers cyclically interconnected to inputs and outputs by way of commutators. Such switches are referred to as rotator switches. Example rotator switches are described in U.S. Pat. No. 4,470,139, entitled Switching Network For Use In a Time Division Network and U.S. Pat. No. 5,168,492, entitled Rotating-Access ATM-STM Packet Switch, the contents of both of which are incorporated herein by reference.
Conventional rotator switches transfer data at a plurality of inputs to tandem buffers each having multiple storage locations. At any time, each input and each output is interconnected with a single buffer. The interconnections of inputs to buffers, and outputs to buffers, are cycled synchronously so that each buffer is interconnected with each input and each output once in a rotator cycle. Data units may be routed from an input to an output, by associating a suitable destination address with each data unit. The destination address may be contained in a header associated with the data unit, or the switch may be configured to statically switch inputs to outputs. Data from any input may be transferred to a storage location within an interconnected tandem buffer, based on its destination. As each tandem buffer is interconnected to an output, a particular one of its locations may be unloaded at that output. For example, the ith storage location of a tandem buffer may be consistently unloaded at the ith output. Each output is associated with a specific storage location in each buffer. The storage location associated with any one output is typically the same for all buffers. Data at an input may quickly be transferred to a destination output by transferring the data to the tandem buffer currently interconnected with the input in the storage location associated with the destination output as indicated by the header, if this storage location is available. When this tandem buffer is next connected to the destined output, the output receives this data.
Now, so that data and associated headers can be switched without delay, and through the switch at the arrival rate, commutators are typically connected to tandem buffers at a rate equal to or in excess of the rate of arrival of data. This, of course, requires careful synchronization between the operation of the commutators and the arrival of data. Moreover, the faster a switch operates the more ancillary difficulties are encountered. For example, faster switches consume more power; require higher tolerance components; are more susceptible to interference; and are more susceptible to parasitic effects of components.
As input line rates have increased to the level of optical line rates, it has become increasingly difficult to manufacture electrical switches, and particularly rotator switches that are able to transfer and switch traffic at the higher rates.
Accordingly, it would be desirable to provide a rotator switch that may accommodate higher line rates, without requiring the switch to operate at significantly increased speeds.